This invention relates generally to grippers and particularly to a sealed, straight line gripper.
It is known in the industry to provide parallel grippers with box-type bodies. These box-type parallel grippers commonly employ a double-acting piston attached to a connecting rod. A cam plate, having angled slots machined therein, forms a wedge. Sliding parallel jaws are attached to the cam plate by pins which are inserted through the angled slots. Typically, these pins are flattened. As the double-acting piston moves in and out, the sliding jaws are forced to close and open with a parallel motion. These traditional bodies and slides have generally rectangular cross sectional exterior shapes. An optional proximity switch is also mounted to the exterior of the gripper body by way of a screwed-on and non-adjustable mounting bracket, which limits the ability to reposition the switch during tool set-up.
Other conventional parallel grippers are constructed with a multitude of complicated linkages, cams and rollers. Examples of such conventional devices are disclosed in the following U.S. Pat. No. 4,892,344 entitled "Parallel Gripper" which issued to Takada et al. on Jan. 9, 1990; U.S. Pat. No. 4,723,806 entitled "Parallel Robotic Gripper" which issued to Yuda on Feb. 9, 1988; U.S. Pat. No. 4,696,503 entitled "Pneumatic Actuated Cam Driven Parallel Gripper" which issued to Collodel on Sep. 29, 1987; U.S. Pat. No. 4,647,100 entitled "Parallel Gripper with Roller Supported Gripper Arms" which issued to Lessway on Mar. 3, 1987; U.S. Pat. No. 4,647,097 entitled "I.D. or O.D. Parallel Gripper" which issued to Lessway on Mar. 3, 1987; and U.S. Pat. No. 4,518,187 entitled "Parallel Movement Gripper Head" which issued to Blaft et al. on May 21, 1985. All of these devices employ a complicated linkage or camming action which make assembly more difficult, are more expensive to machine and increases part costs, while creating durability and accuracy concerns. Additionally, the linkages and cams of these types of traditional grippers enlarge the gripper package, increase the weight, and cause the object being gripped to be an undesirably extended distance away from the piston head. The mechanical moment arm distance between the gripped object and the piston head is thereby increased which reduces the actuating-to-gripping force efficiency and creates tremendous torquing forces on the linkages.
In accordance with the present invention, the preferred embodiment of a straight line gripper employs a longitudinally moving piston head, a laterally moving slide and a drive pin moving the slide in response to movement of the piston head. In another aspect of the present invention, a drive pin is mounted to a piston head and disposed at an angle. In a further aspect of the present invention, a pair of nested slides are moved relative to each other between gripping and ungripping positions by way of outwardly angled drive pins longitudinally moving with a piston head. In yet another aspect of the gripper of the present invention, an external surface of a body and external surfaces of slides are generally circular-cylindrical. An arm is also mounted to each slide in various angular orientations by way of removable locators and a fastener. Another aspect of the present invention provides a booster spring to maintain a pair of gripper arms in gripping positions even when pneumatic pressure is lost. In still another aspect of the present invention, a sensor is mounted to a gripper body only by way of two or more pins retained in an adjacent pair of a set of body holes.
The straight line gripper of the present invention is highly advantageous over traditional constructions. For example, the present invention significantly reduces the number of parts thereby simplifying assembly and reducing part costs while increasing durability and part accuracy through fewer tolerance build-ups. The present invention is also advantageous by providing cylindrical exterior surfaces for the body and slides; these shapes can be easily machined on a lathe in a relatively inexpensive manner. These shapes also encourage easily adjustable mounting.
The specific configuration of the drive pins and slides also allows the center of the gripped part to be positioned within approximately 38 millimeters of the closest point on the front piston head (when disposed in the extended stroke position). This close gripped part-to-piston head distance serves to maximize the gripper's efficiency in the small and lightweight gripper package provided. A double tandem piston can be optionally used to provide additional gripping forces; in this version, the pneumatically powered gripper will provide approximately one kilo-newton of gripping force (using both arms) in response to 5.5 bars (80 psi) of pneumatic pressure input force. By comparison, conventional parallel grippers typically generate less than 625 newtons of gripping force (using both arms) with greater input pressure.
O-ring sealing of the slides assists in maintaining a fully sealed and prelubricated gripper. The present invention is further advantageous by providing interchangeable slides having oppositely angled drive pins and receptacles; this allows for easy reversal of gripping direction given the same piston stroke direction and otherwise identical parts. It is also envisioned that the sections of the drive pins which engage the slides are circular-cylindrical, thereby producing more engagement surface area while preventing the slides from rotating, especially as compared to the traditional flattened pins. This leads to improved positioning accuracy and less part wear. The circular-cylindrical drive pins are also more cost effectively machined. Rotation of the slides and arms is further prevented in the present invention by the use of guiding slots machined in the hardened body. The optional booster spring advantageously prevents the gripper from dropping parts if the fluid power is lost. The present invention gripper is also advantageous over conventional designs by providing an easily adjustable and simple to mount sensor so as to reduce set-up time of the tool and encourage flexibility in the sensor orientation. Additional advantages and features of the present invention will become apparent from the following description and appended claims, taken in conjunction with the accompanying drawings.